Following the March 11, 2011 Tohoku-Pacific Ocean Earthquake, we have designated the entire area of the damaged Fukushima Daiichi Nuclear Power Station as a "Controlled Area" in accordance with the standard set for "Radiation Controlled Areas", and have conducted containment works. Furthermore, given the state of the radiation-infested outside air as well as the radioactive particles that found its way into the building through windows at the early stages of the accident, the Seismic Isolated Building has also been designated a "Controlled Area".
Thus far, in order to improve the safety of the working environment at the Seismic Isolated Building where containment and decommissioning works are being implemented, we have worked to lower the radiation dose rate and improve the level of contamination in the area.
In particular, given the extreme importance of having experienced workers with field experience and specialized knowledge continue on with their supervisory work regardless of whether or not exposure dosage levels exceed 100msV from a safety perspective, we have implemented decontamination countermeasures targeting areas of the Seismic Isolated Building deemed necessary to reduce radiation dosage levels with the goal of finishing such work by the end of the transition period of the special ministerial ordinance*1 (April 30, 2012). As a result, we have confirmed that for the present time, certain areas of the Seismic Isolated Building are able to be treated as an "Uncontrolled area*2.
Thus, as a result of much deliberation, in accordance with the standard set for "Radiation-Controlled Areas we have established certain areas of the Seismic Isolated Building to be treated as "uncontrolled" during operations and prepared a report titled "Treating Certain Areas of Fukushima Daiichi Nuclear Power Station's Seismic Isolated Building as Uncontrolled" that was today submitted to NISA.
We are planning to implement the new rule of treating certain areas of the Seismic isolated building as "Uncontrolled" following arrangements with relevant organizations.
We will continuously work to maintain the stable status of the Fukushima Daiichi Nuclear Power Station, reduce radiation dosage levels in the site and expand the number of "Uncontrolled areas".
○ Attachment
Regarding the status change of certain areas of the Seismic isolated building to "Uncontrolled" (PDF 471KB)
Regarding the treatment of certain areas of the Seismic isolated building of Fukushima Daiichi Nuclear Power Station as "Uncontrolled" (PDF 106KB)
*The attached file(s) titled "Regarding the treatment of certain areas of the Seismic isolated building of Fukushima Daiichi Nuclear Power Station as "Uncontrolled" is only available in Japanese. We apologize for any inconvenience this may cause.
*1 Special ministerial ordinance
The special ministerial ordinance ("Special ministerial ordinance for special provisions of the "Regulation concerning Prevention from Radiation Hazards due to Ionizing Radiation" to respond to the situation caused by the Tohoku - Pacific Ocean Earthquake") was set up to permit the temporary increase of the upper limit of the radiation dose level for workers engaged in emergency works to 250 mSv as long as deemed necessary to prevent the expansion of nuclear damage, in light of the situation at Fukushima Daiichi Nuclear Power Station.
*2 Uncontrolled area
The "Controlled area" is the area, where certain values (radiation dose of external radiation, surface concentration of contamination, radioactive concentration in the air) will exceed or likely exceed the limits specified in the law and requires special control of the radiation exposure. The "Uncontrolled area" is the area other than the "Controlled area".
